The present invention relates to a bearingless rotor blade assembly of a rotary-wing aircraft, and more particularly to a flexbeam assembly having a first beam and a second beam with a pitch shaft channeled therebetween, the beams extend to a radial outboard station of the rotor blade at which the pitch shaft ends and the beams morph into a rotor blade spar.
Conventional rotary-wing aircraft have a forward airspeed limited by a number of factors. Among these is the tendency of the retreating blade to stall at high forward airspeeds. As the forward airspeed increases, the airflow velocity across the retreating blade slows such that the blade may approach a stall condition. In contrast, the airflow velocity across the advancing blade increases with increasing forward speed. Forward movement of the helicopter thereby generates a dissymmetry of lift between the advancing and retreating sides of the rotor. This dissymmetry may create an unstable condition if lift is not equalized across the advancing and retreating sides of the rotor.
A rotary wing aircraft with a contra-rotating rigid rotor system is capable of higher speeds compared to conventional single rotor helicopters due in part to the balance of lift between the advancing sides of the main rotor blades on the upper and lower rotor systems.
Aerodynamic drag associated with a rotary wing aircraft having a counter-rotating, coaxial rotor system is primarily due to the additional rotor hub and the interconnecting main rotor shaft assembly between the upper and lower rotor systems. For high-speed rotary wing aircraft, the increased drag resulting from the counter-rotating, coaxial rotor system may result in a relatively significant power penalty.
The aerodynamic drag of the dual counter-rotating, coaxial rotor system may be reduced by a rotor fairing system. Although effective, sealing compatibility of the rotor fairing system with the rotor blades may be complicated by a relatively thick inboard airfoil section typical of conventional flexbeam rotor systems having an airfoil shaped torque tube that surrounds a flexbeam which receive a pitch input. Sealing with the rotor fairing system may be further complicated by a rotor control system which provides a pitch input to each rotor blade at a location typically adjacent to the interface between the rotor fairing system and each rotor blade.
For a high speed counter-rotating, coaxial rotor system, the advance ratio is sufficiently high such that a significant part of the retreating blade is in reverse flow. Because of the large nose-up cyclic pitch on the retreating blade, the inboard section of the rotor blade has an angle of attack well beyond stall, producing significant negative lift and high drag force. The angle of attack beyond stall, flapping clearances, rotor control system pitch input clearances, and the relatively thick inboard airfoil all combine to complicate fairing system integration and result in degradation of the rotor system lift/drag ratio.
Accordingly, it is desirable to provide a rotor blade for a high speed rotary-wing aircraft flight envelope.